Question

Из двух городов по реке одновременно выплыли навстречу друг другу две моторные лодки. Скорость первой лодки 15км/ч, второй лодки 35км/ч. Первая лодка двигалась по течению реки. Скорость течения реки 5км/ч. Через сколько часов лодки встретились, если расстояние между городами 250км?

Answer 1

250/(15+5+35-5)=5 часов
Ответ 5 часов

Answer 2

Problem Analysis

We have two motorboats traveling towards each other on a river. The first boat has a speed of 15 km/h, while the second boat has a speed of 35 km/h. The first boat is moving with the current of the river, which has a speed of 5 km/h. We need to determine how many hours it will take for the boats to meet, given that the distance between the cities is 250 km.

Solution

To solve this problem, we can use the formula: time = distance / relative speed.

The relative speed is the sum of the speeds of the two boats. Since the first boat is moving with the current, its effective speed is the difference between its speed and the speed of the current. Therefore, the relative speed is calculated as follows:

Relative speed = (speed of first boat - speed of current) + speed of second boat

Let's calculate the relative speed:

Relative speed = (15 km/h - 5 km/h) + 35 km/h = 45 km/h

Now, we can calculate the time it will take for the boats to meet:

Time = distance / relative speed = 250 km / 45 km/h

Calculation

Let's calculate the time it will take for the boats to meet:

Time = 250 km / 45 km/h = 5.56 hours

Answer

The boats will meet approximately 5.56 hours after they start their journey.

Explanation

When the boats start their journey, the first boat will be moving with the current, which will increase its effective speed. The second boat will be moving against the current, which will decrease its effective speed. As a result, the relative speed between the two boats will be the sum of their speeds, taking into account the effect of the current.

By dividing the distance between the cities by the relative speed, we can determine the time it will take for the boats to meet. In this case, the boats will meet after approximately 5.56 hours.

Please let me know if there's anything else I can help you with!